Chlorinated phenols exhibit outstanding germicidal and insecticidal properties and have demonstrated utility as flea repellents, fungicides, wood preservatives, mold inhibitors, etc. In general, effectiveness increases with the degree of chlorine substitution. The commercially available technical grade chlorinated phenols contain some impurities which give rise to objectionable color formation, typically a dark red or dark brown color. The dark color is caused by high molecular weight tarry impurities and is of itself no particular disadvantage for certain applications (fencepoles, housing substructures) wherein the color is relatively unimportant. In many other uses, e.g., in the wood working industry, particularly where painting of the treated product is necessary, a light or water-white colored chlorinated phenol is preferred. Another family of high molecular weight impurities, polychlorinated dibenzo-p-dioxins, is known to have toxic properties. It has also been found that other polychlorinated polynuclear impurities, the chlorinated phenoxyphenols, are a primary cause of blooming of the impure chlorinated phenol. Thus, high molecular weight impurities in chlorinated phenols cause dark coloration, cause blooming and impart toxic properties to the impure chlorinated phenol.
Impurities such as those described above can be removed by distillation of the impure chlorinated phenol. Biltz et al., Berichte 37, 4018 (1904) report the purification of pentachlorophenol by distillation. However, all chlorinated phenols are not completely stable at elevated temperatures and will tend to decompose during storage or distillation to form large volumes of hydrogen chloride and tar. Product degradation is attributed to the presence of metal ions in storage and process vessels and small amounts of catalyst residue, i.e., aluminum and iron chlorides present in the commerical material. Elevated temperatures accelerate the decomposition reactions. Thus, an economical process for purifying chlorinated phenols which simultaneously allows the removal of undesirable impurities and eliminates the decomposition of the chlorinated phenol at the elevated temperatures required for distillation, would be a highly desirable advance in the art for the production of an environmentally safe, aesthetically acceptable, chlorinated phenol biotoxicant.